Interleukin-2 receptors are composed of at least two polypeptide chains of alpha (55KD) and beta (75KD). The IL-2R beta chain is an essential component of the functional receptor for signal transduction of IL-2. We previously reported the distribution of IL-2R subunits among peripheral blood mononuclear cells. We here present some data regarding the expression of IL-2R subunits on various hemopoietic malignant cells. Fresh leukemic cells obtained from adult T cell leukemia patients expressed both alpha and beta chains, and leukemic cells derived from some patients with T cell leukemia, B cell leukemia or myeloid leukemia expressed the alpha and/or beta chain of IL-2R. The IL-2R beta chain on these leukemic cells were demonstrated to be functional for cell growth signaling. IL-2R alpha and beta chains should be tumor markers.